Photoflash network

ABSTRACT

A variable duration photoflash network includes a gas discharge flash tube connected through an SCR to a charge capacitor and a transformer simultaneously applies a triggering signal to the SCR gate and the flash tube trigger electrode. A timing network includes an RC circuit whose resistor is a photoconductor and is initiated and energized with the ignition of the flash tube by the voltage developed across an inductor in series with the flashtube, which voltage charges a capacitor through a rectifier. The RC timing capacitor after the timed interval effects the triggering of an SCR which connects a voltage source across the first SCR in series opposition with the charge capacitor to open the first SCR and extinguish the flash tube.

United States Patent 1 Katayama Aug. 21, 1973 1 PHOTOFLASH NETWORK [75] Inventor: Masayoshi Katayama, Fuchu-shi,

Tokyo, Japan [73] Assignee: Kabushiki Kaisha Sunpack,

Tokyo-to, Japan 221 Filed: Mar. 3, 1971 211 Appl. No.: 120,539

[30] Foreign Application Priority Data OTHER PUBLICATIONS Dale et a1., Semiconductor Power Circuits Handbook Motorola, lnc., 1968, TK 7871.85.M6S; Title Page & pp. 4-3, 4-4, 4-5.

Primary Examiner-Herman Karl Saalbach Assistant Examiner-Marvin Nussbaum Attorney-Stanley Wolder' [5 7] ABSTRACT A variable duration photoflash network includes a gas discharge flash tube connected through an SCR to a charge capacitor and a transformer simultaneously applies a triggering signal to the SCR gate and the flash tube trigger electrode. A timing network includes an RC circuit whose resistor is a photoconductor and is initiated and energized with the ignition of the flash tube by the voltage developed across an inductor in series with the flashtube, which voltage charges a capacitor through a rectifier. The RC timing capacitor after the timed interval effects the triggering of an SCR which connects a voltage source across the first SCR in series opposition with the charge capacitor to open the first SCR and extinguish the flash tube.

Patented Aug. 21, 1973 ATTORNEY PHOTOFLASH NETWORK BACKGROUND OF THE INVENTION The present invention relates generally to improvements in photoflash devices and it relates particularly to an improved gas discharge photoflash network of variable and adjustable flash duration and light amount.

The conventional photoflash network employing a gas discharge flash tube, for example of the xenon filled type, is generally connected across a main capacitor which is charged either by the rectified stepped up voltage of a solid state oscillator or by a rectified voltage derived from the domestic alternating current supply. In this system the flash duration is of the order of seconds and the range of light quantity variation is limited, at its best being of a ratio of 10 to 1. Various networks and expedients have been employed and proposed for adjusting the flash duration and intensity both selectively and in response to the light incident on a photoconductor but these possess many drawbacks and disadvantages. They are generally complicated and expensive systems of little reliability and of limited flexibility and adaptability.

SUMMARY OF THE INVENTION It is a principal object of the present invention to provide an improved photographic photoflash apparatus.

Another object of the present invention is to provide an improved photoflash apparatus employing a gas discharge flash tube.

Still another object of the present invention is to provide an improved gas discharge flash tube apparatus in which the duration of the discharge or flash and the quantity of emitted light is adjustable.

A further object of the present invention is to provide an improved gas discharge flash tube apparatus in which the discharge duration is controlled responsive to the light incident on a photosensitive element.

Still a further object of the present invention is to provide an apparatus of the above nature characterized by its reliability, ruggedness, simplicity, and high flexibility and adaptability.

The above and other objects of the present invention will become apparent from a reading of the following description taken in conjunction with the accompanying drawings which illustrate preferred embodiments thereof.

In a sense the present invention contemplates the provision of an electronic flash network comprising a gas discharge flash tube including a triggering electrode, a source of current, first means for connecting the gas discharge tube to the current source and including a gated electronic switch device having output electrodes connected between the discharge tube and the current source and a gate electrode, a timing network, second means for substantially simultaneously actuating the timing network and applying triggering signals to said gate electrode and triggering electrode to fire and photoflash tube, and third means responsive to the timing network for applying a reverse voltage cut-off signal between said switch output electrodes to open said switch and extinguish the photoflash tube discharge.

Advantageously the electronic device is a solid state or semiconductor switch such as a transistor, SCR, triac or the like and the cut-off signal, in the case of a transistor is applied to the base and in the case of a gated switch such as the SCR the cut-off signal is applied as a reverse voltage across the output electrodes. The timing network is advantageously an RC timing or integrating network in which the resistance element is an adjustable resistance or a photosensitive element and the cut-ofl signal applied in response to the timing network is derived from a capacitor connected to the gated switch in opposition to the current source.

The improved photoflash network is rugged, reliable, simple and of great adaptability and flexibility.

BRIEF DESCRIPTION OF THE DRAWINGS The drawing is a circuit diagram of a photoflash network embodying the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing which illustrates a preferred embodiment of the present invention, a main capacitor 1 which defines a first current source is associated with a suitable charging network in the known manner and stores an electric charge as the flash energy and is connected in parallel to a small-capacity trigger capacitor 2 which defines a second current source through a high resistance resistor 3. A flash tube 4 which consists of a xenon discharge tube of conventional type which is provided with a trigger electrode, and a switching device 5 defining a gated electronic first switch and provided with a gate or control electrode such as, for example, a silicon controlled rectifier device, a thyratron or triac, are series-connected between one electrode of flash tube 4 and one end of the capacitor 1. The other end of flash tube 4 is connected to the other end of main capacitor 1 through an inductance coil 6. A capacitor 8 which defines a third current source is series-connected through a rectifying device 7 across main capacitor 1, and the cathode of a switching device 9 with a control electrode for example a SCR is connected to the junction point of rectifying device 7 and capacitor 8. The anode of switching device 9 is connected to the anode of switching device 5. A secondary coil or winding 10 of a pulse transformer 26 is connected between the control electrode and the anode of switching device 9. A trigger switch 11 together with the primary of trigger transformer 12 are series-connected across trigger capacitor 2. On of the secondary outputs of trigger transformer 12 is connected to the trigger electrode of flash tube 4 as in case of known photographic flashing apparatuses and the other secondary output is applied to between the control electrode and the anode of switching device 5.

A capacitor 14 is connected across reactance coil 6 through a rectifying device such as a diode 13. The constantciirrent regulating or control circuit including a constant-voltage diode is and a transistor 16 is connected, as illustrated, across capacitor 14, and capacitors l7 and 18 for stabilization of the current are connected through said constant-current control circuit. A series circuit, for which the power supply is capacitors 17 and 18, includes one or more light sensitive devices 19, such as photo-transistors, which receive the reflected light from a subject and a time constant or timing capacitor 20. The control electrode of a high input impedance transistor 23 and the bleeder output terminal of a bias bleeder circuit consisting of resistors 21 and 22 are connected to the junction point oflight sensitive device 19 and time constant capacitor 20. Transistor 23 is arranged so that the power supply voltage of capacitors l7 and 18, which is limited by resistors 24 and 25, is applied through the transistor 23 to the primary coil 26 of pulse transformer 26. it should be noted that switching device 5 and inductor 6 define a first means for connecting flash tube 4 across the first current source capacitor 1, transformer 12, capacitor 2, switch 11, diode 13 and capacitor 14 define second means for simultaneously actuating the timing network and applying triggering signals to switching device 5 and the flash tube triggering electrode, and SCR9, transformer 26 and transistor 23 define third means for applying a reverse voltage cut-off signal to switching device 5.

Considering now the operation of the network last described, the switching device 5 is in an open condition after the preceding flashing has been completed. Under this condition, an electric charge is stored in main capacitor 1 by a conventional means. Even when the capacitor 1 is fully charged switching device 5 is still open and the current is not supplied to flash tube 4 or capacitor 14 connected to the flash through rectifying device 13. Accordingly, flash tube 4 does not discharge or emit light and the actuating circuit such as light sensitive device 19, for which the power supply is capacitor 14 is also inactive.

When main capacitor 1 is charged, trigger capacitor 2 and capacitor 8 are charged as specified. When trigger switch 1 l is closed synchronized with the shutter of the camera by a known means, the electric charge in trigger capacitor 2 is discharged through the primary coil of trigger transformer 12. With this operation, one output of trigger transformer 12 is applied across the control electrode and the anode of switching device 5 to close switching device 5 and, at the same time, the other transformer secondary output is applied to the trigger electrode of flash tube 4. Flash tube 4 receives an electric charge from main capacitor 1 which passes through closed switching device 5 as well as a trigger voltage, and discharges and emits light. The instant the flash tube 4 emits light, a counter electromo tive force occurs in reactance coil 6. It charges capacitor 14 through rectifying device 13 and capacitors 17 and 18 under control of the constant-current circuit including transistor 16 and constant-voltage diode 15. At the same time, the voltage is applied to light sensitive device 19 and the measurement of the quantity of light is begun while charging the time-constant capacitor 20 with the control current from light sensitive device 19 which receives the reflected light from the subject upon flashing.

When the quantity of received light, that is, the quantity of light from the flash tube 4 reaches a predetermined level, high input impedance transistor 23 turns on or closes and the current of the stored electric charge or capacitors l7 and 18 flows therethrough. The pulse transformer 26 whose primary coil is seriesconnected to this transistor circuit generates a high voltage pulse signal in secondary coil and turns on switching device 9.

When switching device 9 is turned on, the electric charge stored in capacitor 8 is applied as a reverse bias voltage across switching device 5 in the reverse direction of normal current flow through switching device 9. Accordingly, switching device 5 turns off or is opened during the duration of the flash of flash tube 4 and flash tube 4 stops emitting light by reason of the termination of the discharge therethrough and, the remaining electric charge stays in main capacitor 1.

The computerized electronic flash apparatus of the present invention possesses the advantage that it can control the timing when the light quantity measuring circuit is actuated with the electric signal upon closing of the circuit upon flashing by controlling switching device 5 connected between main capacitor 1 and flash tube 4 so that device 5 makes the circuit only when the flash tube emits light, can synchronize the starting timing of flashing with that of light quantity measurement at all high accuracy, and the construction of the apparatus is simple.

While there has been described and illustrated a preferred embodiment of the present invention it is appar cut that numerous alterations, omissions, and additions may be made without departing from the spirit thereof.

What is claimed is:

1. An electronic flash network comprising a gas discharge flash tube including a triggering electrode, a first current source, first means for connecting said gas discharge tube to said first current source and including a gated electronic first switch having output electrodes connected between said discharge tube and said first current source and a gate electrode, a timing network, second means for substantially simultaneously actuating said timing network and applying triggering signals to said gate and triggering electrode to tire said photoflash tube, and third means responsive to said timing network for applying a reverse voltage cut-off signal between said switch output electrodes to open said switch and extinguish said photoflash tube discharge and characterized in that said second means comprises a second current source, a transformer including a primary winding and a first secondary winding connected to said switch gate electrode and a second secondary winding connected to said flash tube triggering electrode, and means including a switch for connecting said primary winding to said second current source.

2. The electronic flash network of claim 1 wherein said timing network comprises an RC timing circuit including a resistance element and a capacitor.

3. The electronic flash network of claim 2 wherein said RC resistance element is adjustable to vary the time constant of said RC circuit.

4. The electronic flash network of claim 2 wherein said RC resistance element comprises a photosensitive device whose resistance varies with the light incident thereon whereby to vary the time constant of said RC circuit.

5. The flash network of claim 1 wherein said electronic switch comprises a gated solid state switch, said cut-off signal being a pulse signal applied across said device output electrode in a direction opposite to that of the direction of the conduction current therein.

6. The network of claim 1 wherein said third means comprises a third current source, a solid state second switch including a control electrode, means series connecting said first and third current sources, in opposition, and said second switch across said first switch output electrodes, and means responsive to said timing network for applying a triggering signal to said second switch control electrode.

7. The network of claim 6 wherein said first, second and third current sources comprise first, second and third capacitors respectively and comprising means ineluding a resistor for connecting said first capacitor across said first capacitor and means including a diode for connecting said third capacitor across said first capacitor.

8. An electronic flash network comprising a gas discharge flash tube including a triggering electrode, a first current source, first means for connecting said gas discharge tube to said first current source and including a gated electronic first switch having output electrodes connected between said discharge tube and said first current source and a gate electrode, a timing network, second means for substantially simultaneously actuating said timing network and applying triggering signals to said gate and triggering electrode to fire said photoflash tube, and third means responsive to said timing network for applying a reverse voltage cut-off signal between said switch output electrodes to open said switch and extinguish said photoflash tube discharge, said second means comprising an inductor connected in series between said flash tube and said first current source, and means for energizing said timing network including a capacitor and a rectifying device connecting said capacitor across said inductor.

9. An electronic flash network comprising a gas discharge flash tube including a triggering electrode, a first current source, first means for connecting said gas discharge tube to said first current source and including a gated electronic first switch having output electrodes connected between said discharge tube and said first current source and a gate electrode, a timing network, second means for substantially simultaneously actuating said timing network and applying triggering signals to said gate and triggering electrode to fire said photoflash tube, and third means responsive to said timing network for applying a reverse voltage cut-off signal between said switch output electrodes to open said switch and extinguish said photoflash tube discharge and characterized in that said third means comprises a third current source, a solid state second switch including a control electrode, means series connecting said first and third current sources, in opposition, and said second switch across said first switch output electrodes, and means responsive to said timing network for applying a triggering signal to said second switch control electrode.

10. The network of claim 9 wherein said first, second and third current sources comprise first, second and third capacitors respectively and comprising means including a resistor for connecting said first capacitor across said first capacitor and means including a diode for connecting said third capacitor across said first capacitor. 

1. An electronic flash network comprising a gas discharge flash tube including a triggering electrode, a first current source, first means for connecting said gas discharge tube to said first current source and including a gated electronic first switch having output electrodes connected between said discharge tube and said first current source and a gate electrode, a timing network, second means for substantially simultaneously actuating said timing network and applying triggering signals to said gate and triggering electrode to fire said photoflash tube, and third means responsive to said timing network for applying a reverse voltage cut-off signal between said switch output electrodes to open said switch and extinguish said photoflash tube discharge and characterized in that said second means comprises a second current source, a transformer including a primary winding and a first secondary winding connected to said switch gate electrode and a second secondary winding connected to said flash tube triggering electrode, and means including a switch for connecting said primary winding to said second current source.
 2. The electronic flash network of claim 1 wherein said timing network comprises an RC timing circuit including a resistance element and a capacitor.
 3. The electronic flash network of claim 2 wherein said RC resistance element is adjustable to vary the time constant of said RC circuit.
 4. The electronic flash network of claim 2 wherein said RC resistance element comprises a photosensitive device whose resistance varies with the light incident thereon whereby to vary the time constant of said RC circuit.
 5. The flash network of claim 1 wherein said electronic switch comprises a gated solid state switch, said cut-off signal being a pulse signal applied across said device output electrode in a direction opposite to that of the direction of the conduction current therein.
 6. The network of claim 1 wherein said third means comprises a third current source, a solid state second switch including a control electrode, means series connecting said first and third current sources, in opposition, and said second switch across said first switch output electrodes, and means responsive to said timing network for applying a triggering signal to said second switch control electrode.
 7. The network of claim 6 wherein said first, second and third current sources comprise first, second and third capacitors respectively and comprising means including a resistor for connecting said first capacitor across said first capacitor and means including a diode for connecting said third capacitor across said first capacitor.
 8. An electronic flash network comprising a gas discharge flash tube including a triggering electrode, a first current source, first means for connecting said gas discharge tube to said first current source and including a gated electronic first switch having output electrodes connected between said discharge tube and said first current source and a gate electrode, a timing network, second means for substantially simultaneously actuating said timing network and applying triggering signals to said gate and triggering electrode to fire said photoflash tube, and third means responsive to said timing network for applying a reverse voltage cut-off signal between said switch output electrodes to open said switch and extinguish said photoflash tuBe discharge, said second means comprising an inductor connected in series between said flash tube and said first current source, and means for energizing said timing network including a capacitor and a rectifying device connecting said capacitor across said inductor.
 9. An electronic flash network comprising a gas discharge flash tube including a triggering electrode, a first current source, first means for connecting said gas discharge tube to said first current source and including a gated electronic first switch having output electrodes connected between said discharge tube and said first current source and a gate electrode, a timing network, second means for substantially simultaneously actuating said timing network and applying triggering signals to said gate and triggering electrode to fire said photoflash tube, and third means responsive to said timing network for applying a reverse voltage cut-off signal between said switch output electrodes to open said switch and extinguish said photoflash tube discharge and characterized in that said third means comprises a third current source, a solid state second switch including a control electrode, means series connecting said first and third current sources, in opposition, and said second switch across said first switch output electrodes, and means responsive to said timing network for applying a triggering signal to said second switch control electrode.
 10. The network of claim 9 wherein said first, second and third current sources comprise first, second and third capacitors respectively and comprising means including a resistor for connecting said first capacitor across said first capacitor and means including a diode for connecting said third capacitor across said first capacitor. 